Recently, as expectations for high-quality and large-screen TVs such as high-definition TVs have increased, displays suitable for such TVs, such as CRT, Liquid Crystal Display (LCD), and Plasma Display Panel (PDP), have been developed.
CRTs have been widely used as TV displays and excel in resolution and picture quality. However, the depth and weight increase as the screen size increases. Therefore, CRTs are not suitable for large screens exceeding 40 inch in size. LCDs have high performance such as low power consumption and low driving voltage. However, producing a large LCD is technically difficult and the viewing angles of LCDs are limited.
On the other hand, it is possible to produce a large-screen PDP with a short depth, and 50-inch PDP products have already been developed.
PDPs are broadly divided into two types: Direct Current type (DC type) and Alternating Current type (AC type). Currently, PDPs are mainly AC type since these are suitable for large screens.
An ordinary AC PDP includes a front cover plate and a back plate, where partition walls called barrier ribs are inserted between the front cover plate and the back plate to form discharge spaces. Discharge gas is charged into the discharge spaces. The front cover plate with display electrodes thereon is covered with a dielectric glass layer made of lead glass. The back plate is provided with address electrodes, the barrier ribs, and phosphor layers made of red, green, and blue ultraviolet excitation phosphors.
The discharge gas is ordinarily helium (He)-xenon (Xe) or neon (Ne)-xenon (Xe) mixture gas. The gas pressure is set in a range of 500 to 600 Torr to keep firing voltage at 250V or less (see M. Nobrio, T. Yoshioka, Y. Sano, K. Nunomura, SID94' Digest 727-730 1994, for instance).
The light-emission principle of PDPs is basically the same as that of fluorescent lights. That is, in PDPs, voltage is applied to electrodes to generate glow discharges, ultraviolet light is emitted from Xe by the glow discharges, the ultraviolet light excites red, green and blue ultraviolet excitation phosphors, and the phosphors emit visible rays. However, PDPs are not as bright as fluorescent lights due to the low conversion ratios of discharge energy into ultraviolet light and of ultraviolet light into visible rays in the phosphors.
In this respect, "Applied Physics", Vol.51, No.3, 1982, page344-347 describes that a plasma display panel having a gas composition of He-Xe or Ne-Xe uses only about 2% of electric energy for emitting ultraviolet light and only about 0.2% of the electric energy is converted into visible rays (see "Optics Techniques Contact", Vol.34, No.1, 1996, page25, "FLAT PANEL DISPLAY 96'", Part 5-3, and "NHK Techniques Study", 31-1, 1979, page18, for instance).
Regarding this problem, various techniques have been studied to realize discharge panels, such as PDPS, of high panel brightness and low firing voltage by improving the light-emission efficiency.
There are also market demands for such discharge panels. For instance, in current 40-42 inch PDPs for TV sets of National Television System Committee (NTSC) standard, the number of cells is 640.times.480, cell pitch 0.43 mm.times.1.29 mm, and area of one cell about 0.55 mm.sup.2. In this case, PDPs have the panel efficiency of 1.2 lm/w and the panel brightness of 400 cd/m.sup.2 (see FLAT PANEL DISPLAY, 1997, part5-1, page198, for instance).
On the contrary, in 42-inch high-definition TVs that are recently in increasing demand, the number of cells is 1920.times.1125, cell pitch 0.15 mm.times.0.45 mm, and area of one cell 0.072 mm.sup.2. The area of one cell of high-definition TVs is reduced to 1/7-1/8 of that under NTSC. Accordingly, when a PDP for a 42-inch high-definition TV is produced using a conventional cell construction, the panel efficiency and the panel brightness may be lowered respectively to 0.15-0.17 lm/w and to 50-60 cd/m.sup.2.
The panel efficiency of a PDP for a 42-inch high-definition TV, therefore, needs to be improved ten times or more (5 lm/w or more) to acquire the same brightness as that of a current NTSC CRT (500 cd/m.sup.2) (see FLAT PANEL DISPLAY, 1997, part5-1, page200, for instance).
Aside from the improvement in the panel brightness, the white balance needs to be adjusted by improving the color purity to realize a PDP of fine picture quality.
Various studies and inventions have been made to improve the light-emission efficiency and the color purity.
Japanese Patent Publication No. 5-51133, for instance, discloses a PDP that uses three-component mixture gas of argon (Ar)-neon (Ne)-xenon (Xe).
With the mixture gas including argon, the amount of visible rays generated by neon is reduced, so that the color purity is improved. However, the light-emission efficiency is not so improved.
Japanese Patent No. 2616538 discloses a method where three-component mixture gas of helium (He)-neon (Ne)-xenon (Xe) is used.
With this mixture gas, the light-emission efficiency is improved, in comparison with the case where two-component mixture gas of helium (He)-xenon (Xe) or neon (Ne)-xenon (Xe) is used. However, the light-emission efficiency is improved to about 1 lm/w at most in the case of the pixel level of NTSC. Therefore, a technique of further improving the light-emission efficiency is desired.
Regarding the stated problems, the object of the present invention is to provide a gas discharge panel, such as a PDP, where the panel brightness and the conversion efficiency of discharge energy into visible rays are improved and light of fine color purity is emitted.